CODEWITHSUNDEEP
c++qtsleepinterrupt
Johannes Schaub - litb
Johannes Schaub - litb

Reputation: 506995

Interruptible sleep in Qt?

I'm in a worker thread and want to sleep for a specified period of time (usually a few hundreds milliseconds), but the sleep should be interruptible. Here is what I have come up with

void DummyScope::sleepForSamples() {
   if(m_sampleSleep < 100) {
      MySleeper::sleep(m_sampleSleep);
      return;
   }

   // sleep in periods of 100 ms, to be responsible for shutdown requests      
   qint64 t = QDateTime::currentMSecsSinceEpoch();
   qint64 end = t + m_sampleSleep;

   while(t + 100 <= end) {
      MySleeper::sleep(100);
      t = QDateTime::currentMSecsSinceEpoch();

      // TODO: check here whether we are interrupted
   }

   if(end > t) {
      MySleeper::sleep(end - t);
   }
}

However that looks a bit convoluted and I wonder whether there's a better way to do this. Is using a QWaitCondition with a timeout-wait a better solution?

Upvotes: 2

Views: 1116

Answers (3)

alexisdm
alexisdm

Reputation: 29886

You can wait directly on the mutex with QMutex::tryLock(int timeout), if you lock and unlock it from another thread.

Upvotes: 0

stefaanv
stefaanv

Reputation: 14392

Definitely wait on a condition variable and let the accompanying condition tell you why you were interrupted.
If you don't have to use QT-threads, c++11 and boost let you add a predicate to wait_for/timed_wait, so spurious wakeups don't mess with your timeout.

Of course, it is even more convienent if you can go 1 step further and don't bother with a timeout (if the condition variable can handle all cases).

Upvotes: 0

Martin James
Martin James

Reputation: 24857

'Is using a QWaitCondition with a timeout-wait a better solution?'

Yes!

The sleep() loop, apart from needlessly running every 100ms, has an average 'interrupt' latency of 50ms.

Upvotes: 2

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